1. Field of the Invention
The present invention relates to a power source device including a battery pack. More particularly, the present invention relates to a power source device for ensuring worker's safety against electric shock.
2. Description of the Related Art
There are various apparatuses using a power source device including a battery pack. The battery pack has a plurality of battery modules each of which includes a single cell or a plurality of cells connected in series, and which are connected in series. Examples of the apparatuses include an electric vehicle using the battery pack as a driving power source, a hybrid vehicle using the battery pack together with an internal-combustion engine, and other various apparatuses. In such an apparatus, a power switch is provided for opening and closing a circuit for distributing power from the power source device. However, there is a problem such that, while a worker conducts maintenance work or the like with the power switch turned off, the worker may get shocked because of a mistaken power-on operation by another person.
Conventionally, a battery pack provided with a work safety device called as a “service plug” is known as a measure for safety against electric shock (see Japanese Patent Publication No. 2001-320801, for example). In the “service plug,” a safety switch is provided between a given pair of battery modules in the battery pack that are connected to each other. A worker inserts and removes the “service plug” to/from a main body of the switch, thereby connecting and disconnecting the battery modules so as to open and close the power distribution circuit. Moreover, when the worker pulls out the “service plug,” an interlock reed switch is turned off and a system main relay is turned off by a master controller.
By doing so, the worker can remove the “service plug” and conducts maintenance work or the like with safety. That is, even when the power-on switch is turned on by mistake, the power distribution circuit remains open. Therefore, it is possible to prevent the worker from get shocked.
However, anyone can easily insert the “service plug.” Thus, there remains a problem that the worker may get shocked when another person mistakenly inserts the “service plug” while the worker is working and the worker works without noticing the insertion of the “service plug.” Moreover, even if the master controller is configured to turn off the system main relay separately, the system main relay may have a trouble and may be inoperative because of welding or the like. Therefore, it is very dangerous that the “service plug” can be inserted while the worker is working.